1. Field of the Invention
The present invention relates to an audio processing device that performs audio signal processing to a digital audio signal.
2. Description of the Related Art
Conventionally, a digital audio signal to which an audio processing device performs audio signal processing is mainly PCM (Pule Code Module) data (first digital audio signal) in which sampling frequency is 44.1 kHz and the number of quantum bits is 16 bits. In recent years, there has been DSD (Direct Stream Digital) data (second digital audio signal) in which sampling frequency is 2.8224 MHz (=44.1 kHz×64) and the number of quantum bits is 1 bit as digital audio data.
In the audio processing device, in case that a D/A converter that can D/A-convert both PCM data and DSD data is used, noise occurs at timing switching from PCM data to DSD data. In case of PCM data, mute is zero data (a signal is low level.). However, in case of DSD data, when zero data continues to be input to the D/A converter, a signal becomes max level of minus side with full scale. At timing switching from PCM data to DSD data, moment that a signal that is input to the D/A converter is PCM data and the D/A converter is DSD mode that D/A converts DSD data exists. For this reason, an analog audio signal is output from the D/A converter with full scale and noise occurs.
Further, at timing switching from DSD data to PCM data, noise occurs. A mute signal of DSD data is not zero data and a signal of “01101001”, for example. For this reason, in a state that the mute signal of DSD data is input to the D/A converter, if the D/A convertor is switched to PCM mode, noise occurs.
In “About the Way of DoP Method-DSD Native DA Conversion by DA Converter “MY-D3000””, Jun. 11, 2013, to prevent that noise occurs at timing switching from DSD data to PCM data, outputting a signal corresponding to 0V of DSD data (binary digit: 01101001) to a D/A converter is described. However, in such teaching, processing that outputs the signal corresponding to 0V of DSD data is added, and there is a problem that process is complicated.